1. Field of the Invention
The present invention relates to a method for preparing a fluid containing size-controlled particles, thereby establishing a fluid flow of size-controlled particles in a dispersed state. This type of fluid can be used for the particle size calibration (scale adjustment or correction) of particle measurement instruments and for testing the particle collection performance of filters.
2. Description of the Related Art
Light-scattering particle measurement instruments for measuring microparticles in a gas or liquid must be subjected to a particle size calibration prior to use. Fluids that contain size-controlled particles in a dispersed state are used as the standard fluids in these calibrations, and monodispersed particles whose size distribution essentially presents a single peak are used as the size-controlled particles in these standard fluids.
The standard fluids used for the calibration of light-scattering instruments for measuring the particles in a gas typically consist of inert gases containing monodispersed particles of polystyrene latex (PSL). More specifically, standard fluids of this type typically comprise gaseous fluids prepared by spraying a commercially available liquid containing monodispersed PSL particles into an inert gas flow at around atmospheric pressure. Water containing dispersed PSL monodispersed particles is generally employed as the standard fluid for calibrating light-scattering instruments for measuring particles in a liquid.
The particle collection performance of particle-removing filters is tested by passing a standard fluid--in this case a gas containing size-controlled particles in a dispersed state--through the filter. The size-controlled particles used in tests of this type take the form of polydispersed particles whose size distribution essentially presents a plural number of peaks. The use of polydispersed particles and the measurement of the number of particles exiting the filter enables calculation of the collection efficiency at various particle sizes in a single procedure.
The standard fluid (gas) employed in the testing of the particle collection performance of filters typically consists of polydispersed particles of, for example, dioctyl phthalate (DOP) or triphenyl phosphate (TPP), dispersed in N.sub.2 gas. Standard fluids of this type are prepared by spraying an aqueous solution containing the DOP or TPP into a flow of N.sub.2 gas at around atmospheric pressure.
In order to achieve higher measurement accuracies with light-scattering particle measurement instruments, the calibration must be run under conditions approximating actual conditions using the target fluid (i.e., the fluid that will ultimately be subjected to measurement) as the matrix fluid of the calibrating standard fluid. When, for example, the target fluid is a gas such as HCl, HBr, SiH.sub.4, PH.sub.3, or B.sub.2 H.sub.6, one is dealing with reactive gases whose pressure during measurement is typically substantially higher than atmospheric pressure. When the target fluid is a liquid such as H.sub.2 O.sub.2, NH.sub.4 OH, trichloroethylene, or xylene, one is dealing with liquids whose refractive index is different from that of water, which prevents accurate particle size measurement when water is used for calibration. Similarly, in the case of particle-removing filters, in order to obtain agreement between the performance data acquired by testing and the performance data during actual use, the testing must be run under conditions approximating actual conditions using the target fluid (i.e., the fluid that will ultimately be filtered) as the matrix fluid of the standard fluid used for particle collection performance testing.
The use of the target fluid as the matrix fluid under conditions approximating actual conditions causes the following problems for the procedures heretofore used to prepare a fluid containing size-controlled particles. When the target fluid is a reactive fluid, the size-controlled particles can react with the reactive matrix fluid, which can lead to changes in the particle sizes and to the admixture of reaction products into the matrix fluid. In addition, the admixture/dispersion of size-controlled particles into the fluid by spraying results in the admixture of the spray gas into the matrix fluid and hence in a shift in composition. Moreover, this admixture/dispersion method cannot be used when the target fluid is a compressed gas.
The present invention was developed in view of the aforedescribed problems of the prior art. The object of the present invention is to provide a method for establishing a fluid containing size-controlled particles that has been optimized with respect to use of the target fluid as the matrix fluid under conditions approximating actual conditions.